Microwave spectra of the ground and excited vibrational states of isotopic species of nitroethylene

Rotational spectra of nitroethylene, four deuterium and six ¹³C species have been measured and analysed in the frequency range from 8 to 26 GHz. Rotational transitions in the ground state, in progressions of excited states of the NO₂ torsional mode ν₁₈, in the in-plane skeletal bending mode ν₁₃, and in doubly excited states σ₁₃+ν₁₃+ν₁₈ν₁₈ could be assigned for nitroethylene and its deuterated species. The spectra of the ¹³C isotopic species were observed in natural abundance and their assignments have partly been checked by microwave — microwave (mw — mw) double resonance. All the spectra in each of the different vibrationally excited states were found to acceptably obey a rigid rotor pattern with centrifugal distortion, corresponding to a high barrier for the NO₂ internal rotation. Rotational constants and inertia defects all show the same qualitative dependence on the internal state. The ground state rotational constants of all isotopic species have been used to determine a refined molecular structure.     

Mechanism of gas-phase decomposition of nitroethylene: A theoretical study

Calculations by the B3LYP density functional method with various basis sets and by the QCISD(T)/6-31G(d) ab initio method showed that the main pathway of monomolecular gas-phase decomposition of nitroethylene is that involving a cyclic intermediate, 4H-1,2-oxazete 2-oxide; the barrier of its formation (201.9, 203.9, and 216.5 kJ mol^–1, as estimated by various methods) reasonably agrees with the experimental value (191.9 kJ mol^–1). The barriers of alternative pathways of gas-phase decomposition of nitroethylene are considerably higher. The barriers of reactions involving radical cations are considerably lower than those of the similar reactions involving molecules. Among all the considered pathways of nitroethylene decomposition, bimolecular pathways are the most favorable energetically.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 8, 2004, pp. 1327–1342.Original Russian Text Copyright © 2004 by Shamov, Nikolaeva, Khrapkovskii.This revised version was published online in April 2005 with a corrected cover date.     

Radiation-induced postpolymerization of nitroethylene

Radiation-induced postpolymerization of nitroethylene in 2-methyltetrahydrofuran glass has been studied and discussed in reference to the results obtained from ESR measurements. No postpolymerization occurred at the temperature below ?150°C. In the temperature range between ?135°C and ?78°C, the polymer yield decreased with increasing postpolymerization temperature. The polymer yield increased linearly with the increase of the preirradiation dose in the range below 0.9 × 10⁶ r. The mean value for chain initiation was estimated to be about 1.3. The following correlations were observed between the results of the postpolymerization and ESR measurements. The postpolymerization started in the temperature range between ?140°C and ?135°C, where the ESR spectrum due to the anion radicals of nitroethylene disappeared. The polymer yield of the postpolymerization decreased with the photoirradiation at ?196°C before warming the samples in parallel with the photobleachability of the anion radicals observed in the glassy mixture by the ESR method. It was concluded from these results that the radiation-induced postpolymerization was initiated by the anion radicals of nitroethylene formed by the capture of electons.     

The 2B1 ← 2A1 system of nitrogen dioxide

The vibrational structure of the ²B₁ ← ²A₁ system of NO₂ has been assigned to a progression in ν′₂. Vibrational analyses for three isotopic species have been made using a hamiltonian which allows explicitly for a large-amplitude bending vibration. The system origin for the normal isotopic species has been assigned an extrapolated value of 14743.5 cm^?1. The bending potential function is expressed as a rapidly converging Taylor series expansion about the linear configuration. There is no evidence that the equilibrium configuration is nonlinear.     

Microwave spectrum of propionyl chloride

The microwave spectrum of propionyl chloride has been investigated in the region 18.0–40.0 GHz, and transitions due to a cis conformer have been assigned. This form has a heavy atom planar configuration and the methyl group and the carbonyl oxygen atom are cis to each other. Using the substitution structures of propionic acid and acetyl chloride as molecular models for the propionyl chloride molecule, good agreement is found between observed and calculateò effective rotational constants. For the ³⁵Cl species satellite spectra assigned to the first four excited states of the C-C torsional mode have been observed together with the first excited state of the methyl torsional mode. The ground state spectrum has also been assigned for the ³⁷Cl species. Relative intensity measurements yielded the lowest C-C torsional vibration frequency of 86 ± 10 cm^?1. The CH₃ internal rotation frequency was found to be 197 cm^?1. Nuclear quadrupole coupling constants were determined for the ground state of the ³⁵Cl and ³⁷Cl species. From observed A-E splittings of ^bQ-branch transitions of the first excited state of the methyl torsional mode a barrier to internal rotation was estimated to be V₃ = 2480 ± 40 cal mol^?1 (867 ± 14 cm^?1).     

Microwave spectra of [15n] and [13c] pyridines,quadrupole coupling constants,dipole moment and molecular structure of pyridine

The microwave spectra of two ring-substituted species of pyridine have been remeasured, and the spectra of the two remaining species investigated and assigned.¹⁴N quadrupole coupling splittings were analyzed and used to determine the quadrupole coupling constants, while the derived center frequencies were fitted to give improved values for the rotational constants.A complete substitution structure can now be presented.The dipole moment of pyridine was redetermined from Stark measurements in the spectrum of [¹⁵N]pyridine.     

Laser-induced Fluorescence and Dispersed Fluorescence Spectroscopy of NiB: Identification of a New 2II State in 19000-22100 cm-1

The laser-induced fluorescence excitation spectra of jet-cooled NiB radicals have been recorded in the energy range of 19000-22100 cm^-1. Eleven bands have been assigned to the [20.77]²II-X²∑⁺ transition system for the first time. The dispersed fluorescence spectra related to most of these bands have been investigated. Vibrationally excited levels of the ground electronic state, with v" up to 6, have been observed. In addition, the lifetimes for almost all the observed bands have also been measured.     

Conformation,hydrogen bonding and large amplitude motion investigation on N-methylethylediamine by microwave spectroscopy

The microwave spectrum of N-methylethylenediamine and several deuterated species has been investigated in the frequency range 26.5–40 GHz. The rotational spectra of two different conformers with a NH ⋯ N internal hydrogen bond have been assigned. Both conformers have the methyl group trans to the CC bond. The N atom connected to the methyl group acts as proton donor for a conformer (T1), and as acceptor for the second one (T2g). The former is more stable in energy by 0.65(15) kcal mol⁻¹. Rotational lines of several vibrational satellites have been assigned in order to investigate their large amplitude motions and interactions.     

Polarized Raman spectra,thermodynamic functions and bidders to internal rotation of 2,3-dimethoxy toluene

Polarized Raman spectra of 2,3-dimethoxy toluene have been recorded in the region 50–4000 cm⁻¹ and IR spectra in the region 200–4000 cm⁻¹. All the 63 (40a′ + 23a″) normal modes of vibration have been assigned assuming a C_s point group. Consistent assignments for the internal modes of vibration of methyl (CH₃) and methoxy (OCH₃) groups have been proposed. In addition thermodynamic functions have been computed over the temperature range 100–1500 K on a MIGHTY II computer and barriers to internal rotations for the three methyl (CH₃) tops and the two methoxy (OCH₃) tops about their respective axes have been determined, using the assigned torsional frequencies and assumed structural parameter for the 2,3-dimethoxy toluene. The barrier heights have been found to be greater than 2.5 kcal mol⁻¹ for all five tops.     

Studies of Erythrina alkaloids: VII—13C NMR spectral studies of some Erythina alkaloids

A variety of alkaloids have been isolated from the seeds of a range of Erythrina species, including dienoid, alkenoid and lactonic derivatives. The ¹³C NMR spectra of these compounds have been assigned by internal comparisons within this series of related compounds and also by the use of model compounds.     

Hochauflösungs-Protonenresonanz-Spektren von Nitroäthylen, 1-Nitropropen-(1) und 1-Nitropropen-(2)

The proton resonance spectra of nitroethylene, 1-nitropropene-(1), and 1-nitropropene-(2) have been measured in solution with high resolving power at 60 and 100 MHz. A full set of chemical shift and coupling constants, obtained from analysis of the spectra in terms of ABC, ABX₃ and ABCD₂ systems, respectively, is given.     

Isotope shift studies and electronic configuration assignments to the energy levels of neutral erbium

Isotope shifts ΔT (170-166) have been evaluated for 54 even and 94 odd energy levels covering almost all the known configurations of the neutral erbium. These ΔT values have been derived from the isotope shift measurements carried out in 159 lines in the region 3900–4605 A using a Fabry-Perot spectrometer and liquid-air-cooled hollow cathode source with highly enriched ¹⁷⁰Er and ¹⁶⁶Er isotopic samples. Electronic configurations assigned to energy levels of Er I by earlier workers have been mostly confirmed and in few cases revisions have been suggested on the basis of observed ΔT values. Probable configurations have been also suggested for unassigned levels of Er I, and a large number of even levels could be assigned to 4f¹¹ 5d 6s 6p configuration.     

The vibrational spectra of isotopically substituted metal carbonyls : V. C18-O-substituted cis-Mn(CO)4LBr (L = PPh3, AsPh3, SbPh3)

The reactions of cis-Mn(CO)₄LBr (L = PPh₃, AsPh₃, SbPh₃) with 96%¹⁸O-enriched CO in cyclohexane solution at 35°C have been investigated by IR spectroscopy in the ν(CO) region and the vibrational modes of the parent molecules and the various C¹⁸O-substituted species produced have ben assigned with the aid of approximate force field calculations for the energy-factored CO stretching blocks of the (FG) matrices. The IR data for the reaction of the triphenylphosphine complex indicate that, while all four carbonyl groups are eventually replaced by C¹⁸O, there is initially a stereochemical preference for axial CO substitution. For the other two complexes, both carbonyl and L substitution take place.     

Cytotoxic pigments from new zealand sponges of the genus latrunculia : discorhabdins a,b and c

Discorhabdins A, B and C have been isolated as the major cytotoxic pigments of three different Latrunculia sponge species from New Zealand. The ¹H- and ¹³C-NMR spectra of the previously reported discorhabdin C 1 have been assigned. The structures of discorhabdins A 2 and B 3 have been established by spectral comparisons (especially NMR)'with 1. The discorhabdins are strongly cytotoxic (P388 ED₅₀'s 0.03-0.1 μg/ml) and antimicrobial.     

A study of 4-carba-arachno-nonaborane(14) and the derived tridecahydro-4-carba-arachno-nonaborane(−1) anion: Structure and CH bond activation as shown by 1- and 2-D NMR

The ¹¹B and ¹H NMR spectra of the carbaborane CB₈H₁₄, and its anion CB₈H₁₃^?, have been recorded and assigned unambiguously by decoupling and COSY techniques. The results indicate the presence of unsymmetrical bridging hydrogen atoms in both the neutral and anionic species. More significantly the endo-hydrogen attached to the carbon atom is involved in exchange with all the three bridging hydrogen atoms in the CB₈H₁₃^? anion, whereas no such exchange is observed in the neutral CB₈H₁₄.     

The role of the trifluoromethyl group in reactivity and selectivity in polar cycloaddition reactions. A DFT study

The role of the trifluoromethyl group in reactivity, regio-, and stereoselectivity in cycloaddition reactions has been analyzed by studying the 1,3-dipolar cycloaddition (13DC) reactions of nitrone 4 with 3,3,3-trifluoro-1-nitropropene 7b and 3,3,3-trifluoro-2-nitropropene 14 using density functional theory (DFT) methods at the B3LYP/6-311G(d) level. The recent M06-2X functional has also been evaluated but, although the thermodynamic performance is improved, the kinetic data are not necessarily better than those obtained by the popular B3LYP functional for cycloaddition reactions. Four reactive channels associated with the meta and ortho regio- and endo and exo stereoselective approach modes of the nitro group of these disubstituted ethylenes relative to nitrone 4 have been explored and characterized. Unlike other electron-withdrawing groups, the trifluoromethyl group increases the reactivity of the nitroethylene, but it does not modify the meta and endo selectivities when it is located at the β conjugated position of nitroethylene. Analysis of the global and local electrophilicity indices allows for an explanation of the role of the trifluoromethyl group in reactivity and regioselectivity of electrophilically activated ethylenes.     

Exploratory studies towards a total synthesis of the unusual bridged tetracyclic Lycopodium alkaloid lycopladine H

A strategy for a total synthesis of the structurally novel Lycopodium alkaloid lycopladine H has been investigated. Key steps that have been tested include: 1. a regioselective Diels-Alder cycloaddition of nitroethylene with an o-quinone ketal to produce the bicyclo[2.2.2]octane moiety of the alkaloid; 2. a stereoselective Henry reaction to generate the requisite functionality and configuration at C-5; 3. a stereoselective catalytic hydrogenation of a trisubstituted alkene to set the C-15 methyl configuration.     

A vibrational study of the infrared spectrum of dibromodifluoromethane,CBr2F2

The i.r. spectrum of natural dibromodifluoromethane has been recorded at medium resolution in liquid phase and at moderately high resolution in vapor phase. A number of regions have been analysed and the vibrational and vibrational—rotational features of the observed spectral structures interpreted. The frequency values pertaining to the fundamentals of the bromine isotopic species have been either directly measured or evaluated by “difference” bands and their isotopic splitting checked by a normal coordinates calculation. Absorptions due to the minor component ¹³CBr₂F₂ have also been observed and in part assigned.     

Confirmation of the presence of imine bonds in thermally cured polyimides

Model compounds for imines formed during the thermal curing of short chain polyimides have been synthesized and characterized. These compounds have imine bonds (C?N) formed by the nucleophilic attack of primary amines on imide carbonyls. The C?N stretching mode appears at 1649–1664 cm^?1 in the Raman and infrared spectra of these compounds and the band assigned to the carbonyl mode in an imide ring with an imine bond appears near 1740 cm^?1. These compounds have been prepared and characterized to verify the conclusions of a previously reported study in which bands observed in thermally cured short chain polyimides at 1656 and 1742 cm^?1 were assigned as the C?N and associated C?O modes, respectively. It has also been confirmed that the C?N stretching mode in the imide model compounds is inherently IR weak and can only be seen if the concentration of imine species is high. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterization of coordination compounds of organotin(IV) with nitrogen and sulfur donor ligands

The reactions of dimethyltin dichloride with nitrogen and sulfur donor ligands derived by condensation of S‐benzyldithiocarbazate with indol‐3‐carboxylaldehyde, thiophene‐2‐aldehyde and furfuraldehyde have been investigated in 1:1 and 1:2 molar ratios in anhydrous alcohol. These ligands act as mononegatively charged bidentate species and coordinate to the central tin(IV) atom through the thiosulfur by proton exchange with the azomethine nitrogen. The newly synthesized complexes have been characterized by elemental analysis, conductance measurements and molecular weight determinations. The mode of bonding and the geometry of the complexes have been suggested on the basis of infrared, electronic and ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy, and probable structures have been assigned to these complexes. A few representative ligands and their tin(IV) complexes have also been screened for their antifungal and antibacterial activities and found to be quite active in this respect. Copyright © 2001 John Wiley & Sons, Ltd.